Light-beam microphone and method



Jan. n 3,229,098

LIGHT-BEAM MICROPHONE AND METHOD Original Filed April 18. 1960 2Sheets-Sheet l a: -u "5 o 1" n: j A. E "'inr E i i Q .E Ng

1'1"". lr E LI- j INVENToRs. 1 GABRIEL M. GINNINI DELBERT G. VAN ORNUMATTORNEY.

f-I-JF/ l3229998 on maso/wa Jan. ll, 1966 G. M. GIANNINI ETAL 3,229,098

LIGHT-BEAM MICROPHONE AND METHOD 2 Sheets-Sheet 2 Original Filed April18, 1960 lla Fl G. 4. A

/l 22 1NVENToRs-` 'ob F l G' 6 GABRIEL M. GIANNINI DELBERT G. VAN oRNuMATTORNEY.

United States Patent O 3,229,098 LIGHT-BEAM MICROPHONE AND METHODGabriel M. Giannini, Indio, and Delbert G. Van Ornum, Newport Beach,Calif., assignors, by mesne assignments, to Giannini ScientificCorporation, Long Island, N.Y., a corporation of Delaware Continuationof application Ser. No. 22,873, Apr. 18 1960. This application Jan. 15,1963, Ser. No. 252,544 7 Claims. (Cl. Z50-199) This invention relates toa method `and apparatus for transducing air-borne sound vibrations intoelectrical signals through use of a beam of light. The presentapplication is `a .continuation of our co-pending patent applicationSerial No. 22,873, led April 18, 1960 for a Light- Beam Microphone andMethod, now abandoned.

An `object of the present invention is to provide a microphone apparatusand method wherein all equipment may be located a considerable distancefrom the source of sound, so that the problem of excluding a microphonefrom a television picture is eliminated.

Another object is to provide a light-beam microphone and methodcharacterized by a minimum of interference from sounds other than theone which it is desired to transduce into an electrical signal.

A further object of the invention is to provide a method and apparatusfor improving the high-frequency response of a light-beam microphone.

These and other objects and advantages of the invention will be morefully set forth in the following specification and claims, considered inconnection with the attached drawings to which they relate.

In the drawings:

FIGURE 1 is a schematic plan view illustrating a speaker on a stage, andshowing the relationship between such speaker and a rst form ofapparatus embodying the present invention;

FIGURE 2 is an enlarged horizontal sectional view of thelight-transmitting and light-receiving portions of the apparatus;

FIGURE 3 is a vertical section taken on the broken line 3 3 of FIGURE 2;

FIGURE 4 is a view, partially in horizontal section and partially inplan, illustrating a second form of apparatus incorporating theinvention;

FIGURE 5 is a fragmentary end elevation, as viewed from station 5 5 ofFIGURE 4;

FIGURE 6 is a horizontal sectional view illustrating a third embodimentof the invention; and

FIGURE 7 is a vertical section taken on the broken line 7-7 of FIGURE 6.

Referring lirst to the embodiment shown in FIGURES 1-3 of the drawings,the apparatus is illustrated to comprise a light-beam transmitter means10 and a photodetector means 11 so arranged and constructed that soundwaves emanating from a sound source 12 are transduced into correspondingelectrical signals. In the present illustration, the Isound sourcecomprises the vocal cords and mouth of a performer on a stage in atheater, the latter being schematically indicated at 13. The electricalsignals are amplified in suitable amplier means 14 and then conducted toa loudspeaker 15. It is to be understood that the present apparatus andmethod are also adapted for use in television, motion pictures, etc., aswell as 4for technical purposes such as measuring the sound intensity inthe exhaust from a rocket engine.

The transmitter means 10 and photodetector means 11 are disposed closelyadjacent each other in the wing at one side of the stage, and a mirror16 is disposed in the wing at the other side thereof. The means 10 and11 are so related to each other and to mirror 16 that a light beam 17projected from transmitter 10 will be reflected 3,229,098 Patented Jan.11, 1966 ICC back to photodetector 11 for generation of a photoelectriccurrent therein. At least one of the incident and reflected portions ofthe light beam 17 is directed through the air in front of sound source12 and at substantially the same elevation. The beam is accordinglyrefracted correspondingly to the sound waves because of the differentdensities of the air at different portions thereof.

It is pointed out that the sound waves emanating from Isource 12 havethe form of sections of spheres, and comprise a plurality of compressionfronts (such as 18 and 19) separated by low-pressure regions one ofwhich is indicated at 20. The compression fronts 1S and 19 (and thelow-.pressure regions) are spaced substantial distances from each other.For example, the compression fronts of a sound wave having a frequencyof one thousand cycles per second are approximately one foot apart.

It is within the scope of the invention to employ one or more mirrors onthe same side of the stage as the means 10 and 11, in conjunction with acorresponding bank of mirrors adjacent mirror 16. The light beam is thusreflected back and forth across the stage a substantial number of times,in order that the deflection at the photodetector 11 will be increased.It is emphasized, however, that in embodiments wherein the beam of lightis reflected back and forth, different portions of the light beam shouldnot pass through substantially different parts of the sound wave. Thus,it would not be desirable for the incident .portion of beam 17 to passthrough the compression front 1S and the reflected portion of the beamto pass through the front 19. Thus, the transmitter 10 and the detectormeans 11 are located closely adjacent each other, so that both theincident and the rellected beam portions pass through substantially thesame portion of the wave. It is within the scope of the invention toreflect the beam back and forth between mirrors which are so disposedthat the reflected beam portions do not pass through sound wavesemanating from source 12.

Referring particularly to FIGURES 2 and 3, the illustrated transmittermeans 10 comprises a tubular body 22 having a powerful light source 23mounted at one end portion thereof, for example an incandescent lampenergized through leads 24 from a source 25 (FIGURE 1) of electricpower. A mask 26 is mounted in body 22 closely adjacent source 23,having a small hole or opening 27 therein so that a point source oflight is simulated. The illustrated opening 27 is round (FIGURE 3), andshould have a small diameter such as a few thousands or hundredths of aninch. Suitable lens means 28 are provided in body 22 on the oppositeside of mask 26 from source 23, being adapted to transmit light fromopening 2,7 in parallel rays comprising the light beam 17.

The photodetector means 11 comprises a highly sensitive device 30 forgenerating a photoelectric current having an amplitude which varies inaccordance with the quantity of light transmitted thereto. Stated moredeiinitely, the device 30 is a photomultiplier which may be ofconventional construction. Suitable photomultipliers are sold by theRadio Corporation of America under the designations 6199 and 7102. Thephotoelectric current generated in photomultiplier 30 is transmittedthrough leads 31 to the amplifier 14, and thence to the loudspeaker 15or other apparatus such as a radio transmitter.

The photomultiplier 30 is mounted in a tubular body 32 having a mask 33and lens 34 therein. Mask 33 may corerspond exactly to mask 26, and havean opening 36 corresponding to 'opening 27. The lens 34 may correspondexactly to the lens 28 of the transmitter means.

Description of the method, with particular reference to the apparatus ofFIGURES 1-3 In performing the method with the apparatus illustrated inFIGURES 1-3, the transmitter means 10 and photodetector means 11 are soaligned with mirror 16 that the reected portion of light beam 17 will befocused by lens 34 on opening 36 (in complete registry therewith) whenthere is no sound emanating from source 12.

When a compression front (such as is numbered 18 in FIGURE 1) of thesound wave from source 12 passes through the light beam 17, such beamwill be refracted slightly due to the different velocities of light inair having diiferent densities. When the refracted beam (which in theillustrated form is also reected from the mirror 16) is transmitted tothe opening 36 in mask 33, it will be shifted laterally (horizontally)until it is at least partially out of registry with such opening. Thephotoelectric current generated by the photomultiplier 30 is reducedaccordingly.

It is to be understood that if the note from s-ource 12 has a highfrequency, the compression fronts 18 and 19, etc., will be relativelyclose together. The li-ght beam 17 will thus be disturbed relativelyfrequently, so that the resulting photoelectric current will have ahigher frequency corresponding to that of the sound wave. If the notefrom source 12 has a substantial volume, the degree of refraction willbe relatively great and the quantity of light transmitted tophotomultiplier 30 will be diminished accordingly. The amplitude of theA.C. electrical signal will thus be increased. On the other hand, if thenote has a low volume, the degree of refraction of the light beam willbe relatively small, and the quantity of light transmitted to thephotomultiplier will not be reduced by the same degree as when the notehad a strong volume. The A.C. signal will accordingly have a smallamplitude. The device is therefore sensitive to both the frequency andvolume of the sound wave.

Embodment of FIGURES 4 and 5 Referring to FIGURES 4 and 5, a transmittermeans a and photodetector means 11a are illustrated which are adapted totransmit and receive what may be termed a sheet or band of light, asdistinguished from a conventional light beam. Transmitter 10a comprisesa portion 37 containing a light source and a mask corresponding exactly(as to size, construction and location) to elements 23 and 26 shown inFIGURE 2. The forward portion 38 of transmitter 10a has a diameter manytimes that of the portion 37, and contains a large diameter lens 39 anda second mask 41 disposed in advance of such lens.

Mask 41 has a slit 42 therein, such slit being on the order of severalinches or several feet in height but having a width of only a fewhundredths or tenths of an inch. Thus, instead of the conventional beamtransmitted from source 10 of the previous embodiment, the light leavesthe transmitter 10a in the form of a sheet or band which is thin but maybe several feet in height. Such sheet or band is much more thin than thebeam from element 10 of the first embodiment.

Since the width of the slit 42 is very small, and since the distancebetween each compression and the adjacent rarefaction of even a twothousand cycle note is on the order of inches, it will be apparent thatthe light beam has a dimension transverse to the direction of beampropagation which is small in comparison to the distance between eachcompression and rarefaction. Furthermore, as will be set forth below,the beam is in such relationship to the sound waves that the smalldimension of the beam is generally in line with the direction of soundpropagation.

The photodetector means 11a comprises a lens 43 corresponding exactly tolens 39 and adapted to concentrate the light beam onto an opening in amask (unshown) disposed in a small-diameter portion 44 of the detector.Portion 44 also contains a photomultiplier corresponding tophotomultiplier 30 of the previous embodiment. The opening in the mask(unshown) in portion 44 has such a size and shape that refraction of thelight band or beam, as a result of passage of sound waves therethroughfrom source 12, varies the signal generated in the photomultiplier.Thus, assuming that the mask location in detector portion 44 is the sameas that in transmitter portion 37, such opening may be a vertical slithaving a height corresponding to the diameter of opening 27, and a widthjust great enough to receive the entire concentrated beam when no soundis emanating from source 12. The distance from the transmitter anddetector 10 and 11 to mirror 16 may be reduced until only the strongestsound waves cause the concentrated beam to deflect until no part thereofreaches the photomultiplier.

In performing the method with the apparatus of FIG- URES 4 and 5, thelight-beam transmitter 10a is so oriented that the slit 42 and the sheetor band of light transmitted therefrom are generally perpendicular tothe major axis of propagation of the compression fronts, such as 18 and19, emanating from source 12. Thus, when the source 12 is so directedthat the primary sound waves are projected forwardly horizontally,transmitter 10a is so oriented that slit 42 and the sheet or band oflight are vertical. The light band is then tangential to the sphericalcompression fronts.

It is within the scope of the invention to make the slit 42 arcuate asdistinguished from straight, with the radius of curvature being suchthat the light band has approximately the same radius of curvature aseach compression front 18 or 19, etc. The band is then so located thatit is concentric with the compression (or rarefaction) front passingtherethrough. However, the portion of the light band adjacent source 12is still generally perpendicular to the major axis of wave propagationtherefrom.

The light band or sheet transmitted from transmitter means 10a isrefracted by the sound waves and is then received by the photodetectormeans 11a. Lens 43 of such means concentrates the light sheet at theopening in the mask adjacent the photomultiplier. The beam (or a portionthereof) then impinges on the photomultiplier to create an A.C.electrical signal corresponding to the sound waves from source 12.

It is an important feature of the present embodiment that the light beamis very sensitive to the sound waves from source 12, but insensitive tosound waves which travel in directions generally parallel to the lightsheet (for example, vertical) as distinguished from perpendicularthereto. It follows that interference noises are suppressed.

It is another important feature of the embodiment of FIGURE 4 that thehigh-frequency response of the apparatus is excellent. Because of thethinness of the band or sheet of light, it is sensitive to pressurefronts which are only a short distance apart, as is the case with noteshaving high frequencies.

It is to be understood that the means 10a and 11a are arranged, relativeto mirror 16 and source 12, identically to means 10 and 11 of theprevious embodiment.

Embodz'ment 0f FIGURES 6 and 7 In the embodiment of FIGURES 6 and 7, thetransmitter means 10b and photodetector 11b are so constructed andarranged that the response of the photomultiplier to the light beam willbe highly linear at all normal sound volumes, as well as being sensitiveto even the smallest amplitude variations and to high frequencies.Except as will be noted specifically, elements 10b and 11b are identicalto elements 10 and 11 of the embodiment of FIGURES l-3, and have beennumbered correspondingly.

Element 10b is constructed with a mask 46 having a square opening 47therein, two sides of the square being vertical and two sides beinghorizontal. Element 11b is constructed with a mask 48 having acorresponding square opening 49 with vertical and :horizontal sides, butopening 49 is laterally offset (horizontally) from the axis of thedevice. It follows that when the square light beam transmitted fromtransmitter 10b is received by the photodetector 11b, it will not beregistered with the square opening 49 but instead will be horizontallyoifset therefrom as indicated by the numeral 51 in FIGURE 7.

The indicated horizontal offsetting assumes that the apparatus isoriented as shown in FIGURE 1, with the sound source 12 being directedhorizontally and at substantially the same elevation as the light beam.The deection caused by refraction of the light beam is thus horizontalin such manner that there is either a greater or lesser degree ofregistry of the light beam 51 with square opening 49. The result is acurtain or shutter action which is highly linear, and in which at leastpart of the light beam is always registered with the opening 49. Thelinearity results from the fact that a given deection always produces acorresponding percentge change in the area of the beam received by thephotomultiplier.

The sizes of the openings 47 and 49, and the relative locations thereof,are made such that the light beam is never completely out of registrywith the opening 49, regardless of the amplitude of the sound wavetransmitted from source 12. There is thus a modulation action at alltimes, and never a stop-start action.

Various embodiments of the present invention, in addition to what hasbeen illustrated and described in detail, may be employed withoutdeparting from the scope of the accompanying claims.

We claim:

1. A method of transducing audio sound waves into electrical waves,comprising the steps of generating a beam of light having a smalldimension transverse to the direction of propagation of the beam, saiddimension being smaller than the distance between a compression and anadjacent rarefaction of an audio sound wave, passing said beam of lightthrough the open air adjacent a source of audio sound waves travelingthrough said air, and in such relationship to said sound waves that saidsmall dimension is generally in line with the direction of propagationof said sound waves, directing said beam of light to a photodetectormeans whereby said means is caused to generate photo-electric currentcorresponding generally to said sound waves, and amplifying the currentthus generated.

2. The invention as claimed in claim 1, in which said method includesthe step of selectively masking at least portions of said beam of lightprior to irnpingement thereof onto said photodetector means wherebyvariation in the degree of refraction of said beam caused by said soundwaves elects a variation in the degree of masking thereof to thus varythe response of said photodetector means.

3. A method of transducing sound waves into electric current, whichcomprises the Steps of generating a beam having a width which is amultiplicity of times the thickness thereof, directing said beam throughthe air adjacent a source of sound waves traveling through said air andin such relation to said source that said beam is substantiallytangential to a sphere having its center at said source, and disposingphotodetector means in the path of said beam and so constructed thatdeflection of said beam caused by refraction thereof due to said soundwaves varies the response of said photodetector means.

4. A method of transducing sound waves into electrical waves, comprisingthe steps of generating a light beam, transmitting said light beamthrough the air in advance of a source of sound vibrations travelingthrough said air, dispensing a mask in the path of said beam and havingand edge portion which is so constructed and located that it is struckby said beam at all times during passage of normal sound waves throughsaid beam, and disposing photodetector means in the path of the portionof the beam transmitted past said edge portion of said mask.

5. The invention as claimed in claim 4, in which said method includesthe step of correlating the cross-sectional shape of said beam and theshape of said edge portion in such manner that the cross-sectional shapeof the portion of said beam transmitted past said edge portion varieslinearly in accordance with said sound vibrations.

6. A method of transducing sound waves into electrical waves, whichcomprises generating a beam of light, transmitting said beam of lightthrough the ambient atmosphere at a region adjacent a sound-wave sourcewhich is disposed in said ambient atmosphere and which generates in saidatmosphere sound waves adapted to effect refraction of said light beampassing therethrough in said atmosphere, disposing in the path of saidrefracted light beam a photodetector means so constructed thatdeflection of said beam caused by said refraction thereof varies theresponse of said photodetector means, and amplifying the output of saidphotodetector means to provide electrical waves corresponding to saidsound waves.

7. The invention as claimed in claim 6, in which said method furthercomprises the step of shaping said beam of light in such manner that, atleast at the region which impinges against said photodetector means,said beam is a wide, thin band the thin dimension of which is generallyparallel to the direction of propagation of said sound waves.

References Cited by the Examiner UNITED STATES PATENTS 1,709,809 4/ 1929Rashevsky 250-199 2,084,201 6/ 1937 Karolus 88-61 2,362,235 11/1944Barnes 88-141 2,557,974 6/1961 Kibler 250-199 FOREIGN PATENTS 124,805 4/1919 Great Britain.

DAVID G. REDINBAUGH, Primary Examiner. JOHN W. CALDWELL, AssistantExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,229,098 January ll, 1966 Gabriel M. Giannini et al It is herebycertified that error appears in the above numbered peta ent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 6, line l0, for "dispensing" read disposing Signed and sealedthis 21st day of March 1967.

(SEAL) "I Attest:

ERNEST w. SWIDER EDWARD J. BRENNER' Attestng Officer Commissioner oflPatents

6. A METHOD OF TRANSDUCING SOUND WAVES INTO ELECTRICAL WAVES, WHICHCOMPRISES GENERATING A BEAM OF LIGHT, TRANSMITTING SAID BEAM OF LIGHTTHROUGH THE AMBIENT ATMOSPHERE AT A REGION ADJACENT A SOUND-WAVE SOURCEWHICH IS DISPOSED IN SAID AMBIENT ATMOSPHERE AND WHICH GENERATES IN SAIDATMOSPHERE SOUND WAVES ADAPTED TO EFFECT REFRACTION OF SAID LIGHT BEAMPASSING THERETHROUGH IN SAID ATMOSPHERE, DISPOSING IN THE PATH OF SAIDREFRACTED LIGHT BEAM A PHOTODETECTOR MEANS SO CONSTRUCTED THATDEFLECTION OF SAID BEAM CAUSED BY SAID REFRACTION THEREOF VARIES THERESPONSE OF SAID PHOTODETECTOR MEANS, AND AM-